Aluminum, chromium, and gallium tellurates



United States Patent ()filice 3,070,421 Patented Dec. 25, 1962 3,070,421 ALUMINUM, CHROMIUM, AND GALLIUM TELLURATES Gerhard Bayer, Hinteregg, Zurich, Switzerland, assign'or to Owens-Illinois Glass Company, a co oration of Ohio No Drawing. Filed Dec. 7, 1960, Ser. No. 74,226 4 Claims. (Cl. 23-50) This invention relates to new metal tellurates. In a more specific aspect, the invention relates to new compounds of the type A TeO wherein the A atoms have a valence of 3 and the tellurium atoms have a valence of 6, and wherein A is Cr, Al, or Ga.

Rutile-type compounds can be classified into three groups: A4+O A +B +O A +B +O The prototype A +O compound is rutile, TiO A +B +O compounds have the same unit cell and are typified by statistical distribution of the cations in the lattice. Examples include tantalates, such as CrTaO and antimonates, such as AlSbO A +B +O compounds have the trirutile structure as reported by Goldschmidt et al., Geochemische Verteilungsgesetze der Elemente: VI, Uber die Kristallstrukturen vorn Rutiltypus (Geochemical Distribution Law of the Elements: VI, Crystal Structure of Rutile Type With Remarks on Geochemistry of the Bivalent and Quadrivalent Elements), Skrifter Norske Videnskaps-Akad. Oslo, Mat-Nat. KL, No. 1, 21 pp. (1926); p. 18.

The rutile and trirutile structures are closely related. The unit cell of the trirutile structure corresponds to three unit cells of the monorutile structure, except that the Ti positions are occupied in a regular way by A and B ions. Both belong to the space group P4/mm. Prior to my invention only compounds of the general type A +B +O have been found to have the trirutile structure (Anders Bystrom, Brita Hok, and Brian Mason, Crystal Structure of Zinc Metantimonate and Similar Compounds, Arkiv. Kemi, Mineral. Geol., 15B (4) 1-8 (1941); Brian Mason and C. I. Vitaliano, Bystromite, Magnesium Antimonate, a New Mineral, Amer. Mineralogist, 37, 53-57 (1952)).

An object of the present invention is to provide new tellurium compounds containing hexavalent tellurium.

Another object of the invention is to provide new compounds capable of existing in an unusual inverse trirutiletype structure.

Other objects of the invention will become apparent from a study of the accompanying disclosure.

According to the present invention, I have now discovered new metal tellurates of the formula A TeO wherein the valence of the A atom is 3 and the valence of the tellurium is 6. In contrast to trirutile compounds disclosed in the published literature, my present compounds have the general formula A BO The general formula for this compound is in contrast to the general formula AB O for a normal triru-tile compound. The lattice positions of A and B ions are therefore interchanged and the structure of the present crystalline compounds can be interpreted as an inverse trirutile structure. These compounds can be regarded as a superlattice of rutile, with regular distribution of the A and Te ions in the tripled rutile cell.

With B representing Te, the sequence of atomic layers in these compounds is JAABAABAABAAB (A=Al, Ga or Cr; B=Te) as compared to ABBABBABB in normal triru-tile compounds. Disregarding the oxygenions (the 0pararneter should be fairly constant in all compounds), the relative intensities of the same type of X-ray reflection will be determined by the arrangement and the diffracting power of the cations. For the first reflection 002 waves from all the 3-valent ions (A1,Ga, or Cr) oppose to some extent those from the Te-ions. Therefore, this reflection is weakest for the compound containing A(3+) with the highest difiracting power, that is, Ga TeO Values of the atomic scattering factors for this reflection are listed below and compared to the relative intensities.

The relatively high difirac-ting power of Te(6+) is reduced by the diifracting power of the 3-valent ion. Therefore, the reflection 002 is strongest in the compound Al TeO The same is true for the next reflection 101. Also, here planes of Te are interleaved by planes of A-ions (A=A'l, Ga, Cr). The higher the diifracting power of the A-ion, the weaker should be the intensity of this reflection. This is in complete agreement with the observed intensities. In all such cases, Where homogeneous" planes (occupied either by Te( 6+) or by A(3+)) are concerned, the intensities of the reflections decrease in the order I(Al TeO I(Cr TeO I(Ga TeO This is true for 002, 101, 112, 004, 202, 211, and so on. In other cases, where the planes are occupied by both kinds of cations, the reverse order for the relative intensities is found. For these heterogeneous planes, the intensity of reflections is proportional to the mean value of e(f +2f and therefore highest for Ga TeO and lowest for Al TeO Examples are 103 and 200. Al TeO has the smallest lattice constant of all known trirutile compounds.

Each of these compounds was prepared by mixing equimolar proportions of the respective A 0 compound with Te0 The respective oxides were finely divided powders of less than 20 mesh. They were intimately admixed, pressed to a cohesive shape and then fired in an oxidizing (air) atmosphere at 650-700 C. for a period of 20 hours. The A1 0 and Cr O were available, but the Ga O had to be prepared from metallic gallium by dissolving in diluted H precipitating with NH OH, and then calcining.

The oxidizing atmosphere used in firing these A TeO compounds of the invention by the solid-state reaction is necessary in order to convert the tellurium to the hexavalent state. Table I shows the X-ray powder diffraction data, the calculated lattice constants, and the calculated densities of each of the new compounds so prepared. 

1. A COMPOUND OF THE FORMULA A2TEO6, WHEREIN A OS SELECTED FROM THE GROUP CONSISTING OF ALUMINUM GALLIUM AND CARBOMIUM. 